CHAPTER XXIII 

 EXCRETION 



The waste of the body consists mainly of highly oxi- 

 dized products. If the economic ideal were attained 

 these products should represent no potential energy. 

 The major ones do not, but some of the minor ones are 

 susceptible of further oxidation. Carbon dioxid is the 

 foremost product of the metabolism and its removal 

 from the system has been discussed in the chapters on 

 Respiration. 



Water. Water occupies a peculiar position since it 

 may be claimed that it is both a food and a waste. All 

 the water that is taken into the body neglecting that 

 portion which may be added to the tissues during growth 

 will be discharged again. The total output will normally 

 be larger than the intake, for the water that passes into 

 and out from the body has united with it, at the seat of 

 respiration, a moderate amount of water formed by 

 oxidation. This smaller quantity has, of course, no 

 quality to distinguish it from the greater volume of 

 water in which it is merged. At times when the body is 

 gaining water there may be no excess of outgo over 

 income. Water, while in part a waste-product itself, 

 is most useful as a bearer of other waste in solution. 

 It figures thus in the urine and to some extent in the 

 perspiration. 



The chief ways by which excretion can go on are four : 

 by the breathing, the urine, the feces, and the sweat. 

 The order can be defended on the ground that obstruction 

 of the breathing is more immediately fatal than suppres- 

 sion of the urine, while this in its turn is more serious 

 than the failure of intestinal elimination. Contrary 



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